The 555 can be used as a bistable of sorts by connecting a single resistor
between the output and the trigger input. The discharge output is /Q the output
is Q, threshold can be used to force state (esp. reset). The normal input is
through a small capacitor into the trigger input. It can be used as a touch
switch (CMOS 555 and Rfeedback > 2M2). In this case there are two 'meshed'
type touchpads, one supplies +Vcc to trigger through 100K, the other GND. It
can also debounce switches etc.

There are other tricks that can be played using separate +trig and -trig
inputs and Q and /Q (the later with a pullup).

hope this helps ;-)

Peter

PS: There is a book full of 555 circuits but I don't remember where I saw it.
The ideas above are NOT from that book.

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